Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $116.27   9.412%   $127.2133   $127.21   $127.20   $127.20  
  Purchase #2 $239.28   12.296%   $268.7019   $268.70   $268.70   $268.70  
  Purchase #3 $87.57   5.830%   $92.6753   $92.68   $92.70   $92.70  
  Purchase #4 $177.82   11.607%   $198.4596   $198.46   $198.45   $198.50  
  Purchase #5 $213.59   5.638%   $225.6322   $225.63   $225.65   $225.60  
  Purchase #6 $225.90   11.204%   $251.2098   $251.21   $251.20   $251.20  
  Purchase #7 $82.74   12.862%   $93.382   $93.38   $93.40   $93.40  
  7 purchase totals = $1,143.17       $1,257.2741   $1,257.27   $1,257.30   $1,257.30